Heulandite

Chemical Formula: (Ca,Na)2-3Al3(Al,Si)2Si13O36·12H2OLocality: Glasgow, Strathclyde (Dumbartonshire), Scotland.Name Origin: Named after the English mineral collector, John Henry Heuland (1778-1856), a British mineral collector and dealer. Ca modifier added by zeolite nomenclature committee.
Heulandite is the name of a series of tecto-silicate minerals of the zeolite group. Prior to 1997, heulandite was recognized as a mineral species, but a reclassification in 1997 by the International Mineralogical Association changed it to a series name, with the mineral species being named:

Heulandite-Ca

Heulandite-Na

Heulandite-K

Heulandite-Sr

Heulandite-Ba (described in 2002).

Heulandite-Ca, the most common of these, is a hydrous calcium and aluminium silicate, (Ca,Na)2-3Al3(Al,Si)2Si13O36·12H2O. Small amounts of sodium and potassium are usually present replacing part of the calcium. Strontium replaces calcium in the heulandite-Sr variety. The appropriate species name depends on the dominant element. The species are visually indistinguishable, and the series name heulandite is still used whenever testing has not been performed.